"We consider that inciting certain forces within the opposition to boycott the invitation to dialogue is a dangerous path and risks a repetition of the Libyan scenario, which neither Russia nor France wants."

Russia has staunchly opposed attempts by Western governments to push through a UN Security Council resolution targeting President Bashar al-Assad and has circulated an alternative draft calling for him to implement reforms.

European Union nations are considering fresh sanctions against Syria, a diplomatic source who asked not to be identified said in Brussels.

"There is preliminary political agreement" between EU nations on slapping a ban on oil-sector related investment as part of a seventh round of sanctions against the Assad regime, the source said.

Meanwhile, the US ambassador to Damascus, Robert Ford, said in a posting on Facebook that Assad's regime "bears the responsibility for the violence."

The United Nations says 2,200 people have been killed since democracy protests flared in Syria in mid-March.

Activists said the Syrian security forces killed at least 23 more people on Wednesday.

The Britain-based Syrian Observatory for Human Rights said they included 21 people in Homs and two in Sarmeen, in Idlib province in the northwest. The Syrian state news agency, Sana, claimed eight Syrian soldiers and five "insurgents" were killed.

The Local Coordination Committees, which organise the anti-regime protests on the ground, said security forces also killed one person in the central city of Hama.